Aaron Mauger talks up the Champions Cup and Dan Carter

Former All Blacks centre Aaron Mauger believes the European Champions Cup is now the "most prestigious competition" in club rugby.

Mauger helped the Crusaders to four Super Rugby titles between 2000 and 2007, but conceded he feels the tournament has been "diluted" by recent expansion.

The Leicester Tigers head coach will come head-to-head with former All Blacks team-mate Dan Carter in Sunday's Champions Cup semi-final showdown with Racing 92 at Nottingham's City Ground.

Mauger will exploit his inside knowledge of sharing All Blacks and Crusaders backlines with Carter on Sunday, but may cause some raised eyebrows in New Zealand for rating Europe's top club competition ahead of the southern hemisphere's Super Rugby.

"I think the Champions Cup is getting bigger, a bit more so now as I believe Super Rugby has been diluted by adding extra teams, which is a bit of a concern for them down there," said Mauger.

"I think the European competition is probably the higher-quality competition, because you've got all the best teams, especially at this stage, you've got teams who deserve to be there in big games.

"I think it's probably the most prestigious competition.

"The Premiership as well, it might not necessarily be the highest-quality competition, but it's probably the toughest.

"It was a good reflection on Sunday watching Newcastle and Irish battling it out. Two sides who, unfortunately, one will go down.

"It's a good position for English rugby to be in anyway."

Self-confessed "rugby nerd" Mauger claims his parents have photographic evidence of him poring over sporting almanacs as a toddler. The 46-cap centre knew all about Leicester's history when he joined for a three-year playing stint in 2007.

The 35-year-old needed no cluing up then on returning to Welford Road as head coach last summer, charged with adding an expansive edge to Leicester's traditional forward power.

While that studious approach underpins Mauger's coaching, it also meant he knew within seconds of watching a schoolboy Carter that the young fly-half would one day grace the All Blacks.

Some 112 caps and a 2015 World Cup win later, and Carter is thriving at Racing, leaving Mauger wary of his old sparring partner's influence on Sunday.

"The first time I heard of Dan he was playing for Christchurch Boys' High School," said Mauger.

"I was on crutches, I'd broken my ankle in a pre-season game for Canterbury.

"I went down to watch the first XV and he was playing fly-half.

"I knew it wasn't going to be too far away before he was wearing a red and black jersey and a black jersey.

"The next time his name really came up we were on an All Blacks tour watching a Ranfurly Shield match, I think it was Dan's first game for Canterbury, they were playing against East Coast.

"He was playing 12 and I was the All Blacks 12 at the time. Dan scored three tries against East Coast and Tana Umaga was giving me a bit of grief.

"He was saying 'you'd better watch yourself there son, this boy looks like he's keen for your jersey'.

"Every time he stepped up he never looked out of place, he had the feel of the game and that's a great sign for a young player.

"He's never been overawed by any challenge, and it's no different now.

"He's probably been the difference for Racing this year, even though you don't want to pin too much on one person.

"The direction that Dan has given the side has been critical. His composure in those tight moments has been the missing ingredient for them.

"He'll back himself to play what's in front of him, but we've got to back ourselves to take that time and space away from him, limit his options and put him under pressure."